The welding or must high temperature processing of metals, such as steel, must frequently be performed within a carefully controlled environment if any one of a number of matrix altering effects is to be avoided, or is to be permitted. For example, oxidation of the heated surface caused by reaction with ambient air can be avoided by shrouding the work site with a non-reactive gas, such as argon or helium. Likewise, shrouding can be used to prevent detrimental absorption of gases, such as hydrogen, which are present in a moist ambient atmosphere. Shrouding may also be used to introduce a particular gas which is to react with the heated surface in order to modify certain properties thereof.
Shrouding of the work site is normally accomplished by positioning a bowl-like shroud adjacent the work site. The rim of the shroud is normally positioned closely proximate a surface of the workpiece in order to prevent too much of the shrouding gas from prematurely escaping, and thereby unnecessarily increasing the amount of shrouding gas required. The shrouding gas is normally introduced axially parallel to the energy source. The work site area may also be simply blown with one or more jets of shrouding gas. Unfortunately, these jets typically entrain the surrounding environment as they proceed toward the work site area.
Commercial processing, such as welding and the like, of metals is normally performed on a relatively large scale. Large scale processing normally requires that there be relative motion between the energy source and the workpiece. This relative motion can be brought about by movement of the energy source, as well as the associated shrouding mechanism, or by movement of the workpiece.
Movement of an object, such as a workpiece, in a particular direction within a fluid, such as the ambient atmosphere, causes a relative fluid motion to be induced over the workpiece surface in the opposite direction. The induced flow can result in contamination of the confined shrouding gas by permitting the surrounding fluid environment to be introduced into the shroud, and thereby contaminating the shroud environment. High jet velocities have been used as one means for reducing contamination when relatively high processing speeds are required. High jet velocities can be detrimental, however, by affecting the flow of the molten material within the heated area. Molten metal flow abnormalties can be particularly detrimental in applications such as cladding of the workpiece by laser processing and the like.
The disclosed invention is a gas shroud and method which is particularly suitable for situations wherein there is relative motion between the energy source and the workpiece. The disclosed invention incorporates a shroud which is rotatable on an axis for causing the ambient environment to be expelled radially away for thereby offsetting the induced fluid motion.